Apparatus for agitating developer material within a housing

ABSTRACT

An apparatus for developing a relatively moving surface bearing a latent electrostatic image wherein the apparatus includes a housing supporting developer material in contact with the surface. The motion of the image-bearing surface with respect to the development housing effects a frictional coupling of the development material therein to cause a circulation of developer for development of the latent image. The development apparatus further utilizes a moveable magnetic field producing means mounted exteriorly of the housing to increase the circulation of developer to produce enhanced development results over extended periods of use.

115] 3,641,977 Feb. 15, 1972 3,117,891 Lehmann...

[54] APPARATUS FOR AGITATING DEVELOPER MATERIAL WITHIN A HOUSING Primary Examiner-Mervin Stein [72] Inventor: Frederick W. Hudson, West Henrietta, A i tant Examiner-Leo Millstein Attorney.lames J. Ralabate, Donald F. Daley and Robert W. Mulcahy [73] Assignee:

[22] Filed:

[ ABSTRACT An apparatus for developing a relatively moving surface bear- 2] A LN .2 14 927 l 1 PP 0 ing a latent electrostatic image wherein the apparatus includes a housing supporting developer material in contact with the 52 u.s.c|......

.1 18/637, 1 17/ 1 7 .5 surface. The motion of the image-bearing surface with respect ,,G03g 13/00 to the development housing effects a frictional coupling of the 118/637, 637 X; 1 17/175; development material therein to cause a circulation of developer for development of the latent image. The develop- [51] lnt.Cl. [58] Field of Search 346/74 MP; 355/3; 259/DlG. 46

ment apparatus further utilizes a moveable magnetic field producing means mounted exteriorly of the housing to in- Reierences Cited crease the circulation of developer to produce enhanced development results over extended periods of use.

UNITED STATES PATENTS Drexler............;.....................

1 18/637 8 Claims,"5 Drawing Figures PAIHIMFEB 15 B72 SHEET 1 BF 2 .9 vc an n uu anm.

INVENTOR.

FREDERICK W. HUDSON ATTO EY' APPARATUS FOR AGITATING DEVELOPER MATERIAL WITHIN A HOUSING BACKGROUND OF THE INVENTION This invention relates in general to developing latent electrostatic images and, in particular, to an apparatus for supporting developer material in contact with a moving photosensitive surface for development thereof.

More specifically this invention relates to a development apparatus wherein developer is supported in contact with a moving image-bearing surface by a housing whereby the frictional coupling of the developer to the surface and gravity combine to circulate developer in the housing. A moveable member having a magnetic field producing means controls the degree of agitation of the developer in the development housing to produce more effective development results.

In the process of xerography, a xerographic plate comprising a layer of photoconductive material on a conductive backing is given a uniform electric charge on its surface and then is exposed to subject matter to be reproduced by various projection techniques. This exposure discharges the plate in accordance with the light intensity reaching it thereby creating a latent electrostatic image on or in the plate. Development of the image is effected by developers which may comprise, in general, a mixture of suitable, pigmented or dyed, resin base powder, hereinafter referred to as toner, which is brought into contact with the plate by various well-known development techniques. During such development of the image, the toner powder is brought into surface contact with the photoconductive coating and is held there electrostatically in a pattern corresponding to the latent electrostatic image. Thereafter, the developed xerographic image may be transferred to a support material to which it may be fixed by any suitable means such as heat fusing.

Various development devices have been utilized in xerography to develop a latent electrostatic image formed on a photosensitive surface. One well-known technique of development is disclosed in U.S. Pat. No. 2,573,881 to Walkup et al., wherein toner carried by carrier particles is rolled or cascaded over the latent electrostatic image bearing surface. The carrier and toner materials are selected so that triboelectric attraction exists between them causing the two particles to cling together and acquire an opposite charge. In practice, each carrier has numerous toner particles attracted thereon which are brought into contact with the photoconductive surface. During contact with the photoconductivesurface the greater electrostatic attraction of the latent image overcomes the triboelectric attraction between the two developer components causing toner to be stripped off the carrier and electrostatically bonded to the charge image to effect development thereof,

Although cascade development produces satisfactory results, several difficulties are associated with the cascade .method of development. Cascade development, for example,

requires bulky and expensive conveying mechanisms to transport the developer past the latent image and to be circulated again in the system. Further, cascade development requires a thorough intermixing of developer after repeated development of an image. If such intermixing does not occur, a defect in development referred to as image striations results because of localized carrier material becoming depleted of toner powder. Normally, toner depletion occurs in cascade development when the carrier and toner materials move past the image in one direction along the direction of the flow, and repeated development causes the developer flow moving past the more massive image areas to be depleted of toner in a greater amount than the less massive areas thereby causing certain areas of the developer flow to be depleted of toner more than others. Therefore, elaborate intermixing systems are required to overcome this toner depletion problem.

Another problem associated with the cascade technique of development results from the inherent impact of the developer upon the image bearing surface being developed. Such an impact of developer material tends to dislodge toner particles from the carrier whereby toner is readily attracted to nonimage or background areas of the image-bearing surface because of their separation from the triboelectric attraction of the carrier particles. Moreover, the impact of developer on the image-bearing surface effects adislodgement of toner already adhering to the electrostatic image to produce and undesirable removal of toner.

One attempt to overcome some of the aforementioned problems presented by the cascade technique of development is disclosed in the copending application Ser. No. 528,846 by Robert W. Gundlach filed on Feb. 21, I966, now U.S. Pat. No. 3,503,776 wherein a gentle technique of development is provided. Such a development system includes a housing supporting a supply of developer material which is in contact with a moving photosensitive surface to be developed whereby the movement of the surface creates a frictional coupling with the developer in contact therewith to result in a circulation of developer within the housing for development of the image.

Further, the simplicity of the system in the aforementioned copending application results in an inexpensive development apparatus which achieves a self-contained circulation of developer without requiring elaborate buckets and other conveying mechanisms normally necessary in a cascade development device. Also, this development technique effects a gentle contact of developer onto the image-bearing surface and thus prevents background deposition and removal of toner already adhering to the image as occurs in other forms of development.

Although the novel method and apparatus in the aforementioned application by Gundlach produces the above-mentioned advantages and other improvements over prior art development methods, it is desirable to increase the circulation of developer within the housing of such a development technique. Since the movement of developer in the system depends on the motion of the surface to be developed and gravity to achieve a circulation of developer, the degree and amount of circulation is thereby relatively limited. By increasing the circulation of developer in a development apparatus dependent only on the motion of the image surface and gravity for agitation, the creation of voids or pockets of stagnant developer material is prevented. Such an increase of circulation of developer insures that carrier particles adjacent the image are adequately and selectively exchanged with the underneath levels of the developer within the housing in order that adequately tonerized developer is maintained adjacent the image during extended development intervals. Accordingly, it is advantageous to improve prior art development techniques by providing a development apparatus which achieves sufficient agitation of developer within a self-circulating and noncomplex development apparatus.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to develop a latent electrostatic image with an improved apparatus.

Another object of this invention is to develop a latent electrostatic image with an apparatus having a minimum degree of complexity.

A further object of this invention is to eliminate abrasive and abrupt impact of developer material on an image-bearing surface to be developed.

Still another object of this invention is to control the amount and degree of agitation of developer material within a housing.

These and other objects are attained in accordance with the present invention wherein there is provided an effective development apparatus which overcomes many of the aforementioned difficulties presented by prior art development systems. The invention includes a housing which supports developer material in contact with a moveable image bearing surface. The housing is so situated that the combined effect of the motion of the image-bearing surface and gravity effects a circulation of developer within the housing for development of the image. The present invention further includes a control means mounted adjacent the housing to. increase the circulation and agitation of developer therein and insure that adequately tonerized carrier particles are brought into development contact with the surface to be developer. Ac cordingly, a substantial degree of circulation and agitation of developer material is achieved by the apparatus of the present invention wherein the combined effect of gravity, the frictional coupling of the surface to be developed with developer material in contact therewith, and the control means produces a gentle development system which provides enhanced development results over prior art devices.

Accordingly, the present invention is a noncomplex and economical technique for developing an image without producing adherence of toner in background or nonimage areas or the abrading dislodgement of toner from developed areas. The provision of the control means in the present invention insures that the carrier particles within the housing are sufficiently agitated to such a state that substantially all the material within the housing is circulated for development contact. By agitating most of the developer in the housing, the problem of toner depleted carriers remaining in development contact with the image is minimized thus to bring adequately tonerized carrier particles in the vicinity of the image for maximum development results. The control means herein disclosed comprises a field-producing means which influences developer material in such a manner to cause considerable agitation or circulation thereof and as a result, the present invention achieves improved development with a system having a minimum ofcomplexity.

Further objects of this invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of several embodiments of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic illustration ofa drum-type xerographic machine utilizing the development apparatus of the present invention;

FIG. 2 is a schematic illustration of an embodiment of the development apparatus according to the present invention;

FIG. 3 is a schematic illustration of another embodiment of the development apparatus according to the present invention;

FIG. 4 is a schematic illustration of still another embodiment of the development apparatus according to the present invention;

FIG. 5 is a schematic cross-sectional view of the developer agitation device taken along lines 5-5 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. i, there is shown a schematic view of a drum-type xerographic machine utilizing the development device of the present invention. The central element of the machine is a drum I mounted by suitable means and drivable in a clockwise direction by a motor (not shown). The drum ll comprises an outer surface with a layer of photoconductive insulating material such as vitreous selenium or any other suitable surface. A uniform electrostatic charge is placed on the photoconductive surface of the drum l by means ofa conven tional corona charge device 2. The uniformly charged surface is then moved to exposure means 3 which may be any wellknown device which will expose the charged surface to copy to be reproduced and form a latent electrostatic image of the copy on the photosensitive drum surface.

Following the formation of the latent electrostatic image of a copy, the image on the drum moves to development device according to the present invention (to be described in detail later) to bring the latent electrostatic image in contact with developer material comprising, for example, carrier particles and electroscopic toner for development thereof. After development, the visible image moves to a transfer means 4 and is transferred from the drum to a web of paper 5 or the like which is positioned into contact with the drum by a roller 16. The roller is connected to a suitable electrical bias to apply a field to the back of the support material to facilitate transfer of the toner powder in image form. The toner image transferred to the web then moves past a suitable fusing element (not shown) which permanently affixes the toner to the paper web to form a duplicate of the original copy. A rotating brush 7 contacts the drum surface after it moves past the transfer device 4 to remove any residual image material on the surface prior to a subsequent reproduction cycle. While reference has been made to specific components in the reproduction cycle, it should be understood that other modes of charging, exposing, transfer, or fusing may be utilized in connection with the present invention.

Referring now to FIG. 2 there is illustrated one embodiment of the development device 10 of the present invention. The development device 10 comprises a housing 11 positioned by suitable mounting means (not shown) adjacent drum 1 having a latent electrostatic image to be developed. The housing 11 extends along a segment of the drum surface whereby end 12 of the housing is elevated in reference to end 13. The latent image on the photoconductor surface rotates in a clockwise direction to pass the development device 10 for development thereof. The interior of the housing 11 supports a supply of developer material wherein the housing is suitably sealed by means (not shown) to prevent the loss of developer to the exterior of the development device. The developer material supported in the housing comprises a suitable developer such as, for example, carrier particles and electroscopic toner and a sufficient supply thereof is utilized to substantially fill the interior of the housing so that the moving surface of the drum contacts the developer material therein.

As the drum rotates into contact with the developer material within the housing 111, the layers of developer nearest to the drum surface are coupled by frictional forces to the drum surface. Therefore, as the drum surface bearing a latent image is rotated past the housing, the layers of developer material are moved from the lower portions of the housing to the more elevatedportions thereof whereby toner is stripped from the carrier particles by the electrostatic force field of the latent image for development thereof. At the same time, developer material in the elevated portions of the housing tend to drop by gravity along the backwall 14 of the housing and thus a circulation of carrier and toner is achieved in the development device upward along the drum and down wall 14. However, even though the combined action of the frictional coupling and gravity produces the aforementioned agitation of developer, it is advantageous to increase the circulation of developer within the system to prevent only localized carrier particles being in development contact with the image which beads would readily become depleted of toner after extended development intervals. Accordingly, developer circulating device 20 is provided to increase the control of the circulation and agitation of developer within the housing and insures that the entire supply of developer comes into development con tact with the image surface.

The developer circulating device 20 comprises a plurality of parallel belts 21 suitably mounted adjacent the backwall 14 of housing 11 on idler rollers 22 and a driver roller 23 whereby the drive roller drives the belts in a direction to correspond to the movement of developer effected by gravitational forces along the backwall. The idler rollers 22 and drive roller 23 support the plurality of belts in a parallel relationship in selected close proximity to each other in such a manner to facilitate the belts conforming to the curvature of the backwall M. Each belt 21 supports a plurality of magnet means such as, for example, small permanent magnets 25 having a North pole 26 and South pole 27 oriented in the direction of movement of the belt to create an alternating magnetic field with respect to the developer. The magnets are carried by each belt along the entire length thereof and the magnets may be any selected width, such as, the width illustrated in FIG. 5 equaling approximately the width of the belt. As further shown in FIG. 5, drive roller 23 is conventionally coupled to a suitable motor means 24 to drive the belts 21 in the selected direction to create the desired alternating magnetic field within the housing. Any number of magnets may be carried by each belt depending on the desired agitation of developer within the housing. It should also be apparent that the magnets may be carried on any selected number of parallel belts including a single belt which extends a substantial width of the housing wherein, in such a case, the magnet means likewise is of a width substantially equal to the housing. The magnets are suitably secured to the belt surface in any conventional manner as illustrated in FIG. 5. Therefore, in the embodiment of FIG. 2, a plurality of magnets are mounted on respective moving belts whereupon an alternating magnetic field is applied to the developer to increase the circulation thereof within the housing.

The magnetic field produced by the developer circulating device induces the levels of developer along the backwall 14 to move along the housing and increase the circulation of developer therein. The speed of the belt may be selected by control of the motor 24 to create the desired degree of movement and agitation of developer on the backwall. Therefore, through the combined effect of gravity and the magnetic field of the belts 21, a significant degree of control of the movement of developer within the housing is achieved by the present invention to insure that substantially all the carrier beads within the developer mixture are circulated into contact with the photoconductive surface for development. When utilizing the development circulating device 20 of the present invention, it is desirable to utilize a developer mixture comprising a suitable carrier particle having ferromagnetic properties to be adequately influenced by the movement of the magnetic field relative thereto. Any conventional ferromagnetic carrier may be utilized in conjunction with the present invention to produce the desired circulation and agitation of developer under the influence of the magnetic field. Therefore, the circulating device of the embodiment of FIG. 2 increases circulation of developer in the back levels of the housing and as a result, greater agitation of the developer is achieved throughout the housing due to the increased circulation along the backwall.

Referring now to FIG. 3 there is illustrated another embodiment of the development device of the present invention. The development device of the embodiment of FIG. 3 is identical to that described in reference to FIG. 2 except that a developer circulating device 30 is located within the photoconductor drum to increase the agitation of developer within the housing 11. The developer circulating device 30 of the embodiment of FIG. 3 comprises three idler rollers 31 and a drive roller 32 supporting a plurality of parallel belts 33 having an array of magnets thereon to provide an alternating magnetic field within the housing. The belts are moveable at a selected speed through the power supplied by a suitable motor means (not shown) coupled to the drive roller, similarly as illustrated in reference to FIG. 5, to produce a motion of the belts in a direction corresponding to that of the drum surface. A magnetic field emanates from the belts 33 from magnetic means 34 such as, for example, permanent magnets which are carried thereon in a manner such as described in reference to FIG. 2. Similarly, any selected number of belts and magnets may be utilized in the embodiment of FIG. 3 of the present invention depending on the desired strength of the field and agitation of developer. The movement of belts 33 in the direction of movement of the image aids in agitating and carrying the material along the drum surface in an upward direction. Accordingly, circulation of developer within the entire housing is increased by such an increase of the movement of developer frictionally coupled to the drum surface. By selecting the speed of the belts and the strength of the magnetic field means 34, a significant degree of control of the agitation of developer within the housing is achieved by the present invention.

Referring now to FIG. 4 there is illustrated another embodiment of the development device 10 of the present invention. The embodiment of FIG. 4 is identical to the embodiment illustrated in reference to FIG. 2 except that it further includes the developer circulating device 30 illustrated in reference to FIG. 3 located within the drum 1. Accordingly, circulation of developer is increased in the embodiment of FIG. 4 upward along the drum by circulation device 30 and down the backwall of the housing by circulation device 20 to produce increased circulation in both directions. The additive utilization of the two developer circulating devices of the embodiments of FIGS. 2 and 3 significantly increases the developer circulation to aid in the development of an image through the combined influence of the frictional coupling of the moving surface through the bed of developer material, the effects of gravity upon developer in the elevated positions of the housing and the motion induced by the two field-inducing devices 20 and 30 located within the drum and exteriorly of the housing. The amount of agitation may be selectively controlled by independently adjusting the speed of the belts 21 and 31 and the strength of the magnetic field thereon.

In the above description there has been disclosed an improved apparatus for effectively developing an electrostatic image supported on a xerographic photosensitive surface. The surface to be developed has been described for convenience of illustration as being that of a xerographic drum, but the invention may be used to develop other well known photosensitive members in the form of plates, belts, webs, or coated papers. It is further within the scope of the present invention to transport the belt carrying the field-producing means in different directions than as herein disclosed and any speed thereof may be utilized wherein the direction and speed selected depends on desired development results. Further, the magnetic field carrying means of the developer circulating device of the present invention has been illustrated as comprising a belt, but it is within the scope of the present invention to employ any means to aid in the circulation of developer which tends to move relative to the housing. Such other forms to carry the magnetic means may encompass cylinders for carrying magnets, rotary magnets, and the like. Also, it should be apparent that the magnets illustrated for producing the relatively moving field of the present invention are oriented in the direction of movement of the members supporting it, but the poles of the magnets may be oriented in other directions to accomplish the result of controlling the agitation of developer within the housing. Furthermore, the magnetic field producing means may comprise other well-known field-producing devices other than permanent magnets such as, for example, electromagnets and the like.

While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

What is claimed is:

1. Apparatus for developing a surface bearing a latent electrostatic image comprising,

a housing containing a quantity of developer material supported adjacent the surface to be developed to create a frictional coupling between said surface and a portion of the developer material in said housing,

means for imparting a relative movement between said housing and said surface to be developed to agitate portions of the developer material within said housing into contact with said surface,

field-generating means including an array of flux-producing elements mounted adjacent the exterior of said housing adapted for movement relative to said housing to apply an alternating magnetic field on said developer material to increase the agitation of the supply of developer material supported in said housing and enhance development of the imageibearing surface and,

means for imparting a movement of said array of fluxproducing elements relative to said housing.

2. Apparatus for developing a surface bearing a latent electrostatic image comprising,

a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing,

means for advancing said surface to be developed in relation to said housing to produce an agitated movement of portions of the developer material within said housing,

field-generating means including an array of flux-producing members exterior of said housing adapted for movement relative to said housing for applying alternating magnetic fields to influence portions of the developer material contained therein. and

means for producing a movement of said array of fluxproducing members relative to said housing to produce an additional agitated movement of the developer material within said housing and enhance development of the image-bearing surface.

3. Apparatus for developing a surface bearing a latent electrostatic image comprising,

a housing containing a quantity of developer material supported adjacent the surface to be developed to create a frictional coupling between said surface and a portion of the developer material in said housing,

means for imparting a relative movement between said housing and said surface to be developed to agitate portions of the developer material within said housing into contact with said surface,

field-generating means including an array of flux-producing elements positioned in opposing relationship to said housing to allow the image-bearing surface to pass between said housing and said field-generating means, said fieldgenerating means being adapted for movement relative to said housing to apply an alternating magnetic field on said developer material to increase the agitation of the supply of developer material supported in said housing and enhance development of the image-bearing surface, and

means for imparting a movement of said array of fluxproducing elements relative to said housing.

4. Apparatus for developing a surface bearing a latent electrostatic image comprising,

a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing,

means for advancing said surface to be developed in relation to said housing to produce an agitated movement of portions of the developer material within said housing,

field-generating means including an array of flux-producing members positioned in opposing relationship to said housing to allow the image-bearing surface to pass between said housing and said field-generating means, said field-generating means being adapted for movement relative to said housing for applying alternating magnetic fields to influence portions of the developer material contained therein, and

means for producing a movement of said array of fluxproducing members relative to said housing to produce an additional agitated movement of the developer material within said housing and enhance development of the image bearing surface.

5. Apparatus for developing a surface bearing a latent electrostatic image comprising,

a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the develtziper material in said housing, means for a vancmg the surface to be eveloped relative to said housing to produce a circulating agitation of the developer material within the housing to develop the image, and

magnetic field producing means in cooperative association with said housing for impressing magnetic attractive forces on developer material within said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the imagebearing surface.

6. In an apparatus for developing a surface bearing a latent electrostatic image in which a housing containing a quantity of developer material is supported adjacent the surface to be developed to form a frictional coupling between the surface and a portion of the developer material in the housing, and the surface to be developed is advanced in relation to the housing to produce a circulating agitation of the developer material within the housing to develop the image, the improvement comprising,

magnetic field producing means for exerting a magnetic attractive force on developer material within said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface.

7. Apparatus for developing a surface bearing a latent electrostatic image comprising,

a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing,

means for advancing the surface to be developed relative to said housing to produce a circulating agitation of the developer material within the housing to develop the image,

magnetic field producing means including an array of fluxproducing members in cooperative association with said housing for impressing magnetic attractive forces on developer material within said housing, and

means for producing a movement of said array of fluxproducing members relative to said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface.

8. In an apparatus for developing a surface bearing a latent electrostatic image in which a housing containing a quantity of developer material is supported adjacent the surface to be developed to form a frictional coupling between the surface and a portion of the developer material in the housing, and the surface to be developed is advanced in relation to the housing to produce a circulating agitation of the developer material within the housing to develop the image, the improvement comprising,

magnetic field producing means including an array of fluxproducing members in cooperative association with said housing for exerting magnetic attractive forces on developer material within said housing, and

means for producing a movement of said array of fluxproducing members relative to said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface.

nlao 

1. Apparatus for developing a surface bearing a latent electrostatic image comprising, a housing containing a quantity of developer material supported adjacent the surface to be developed to create a frictional coupling between said surface and a portion of the developer material in said housing, means for imparting a relative movement between said housing and said surface to be developed to agitate portions of the developer material within said housing into contact with said surface, field-generating means including an array of flux-producing elements mounted adjacent the exterior of said housing adapted for movement relative to said housing to apply an alternating magnetic field on said developer material to increase the agitation of the supply of developer material supported in said housing and enhance development of the image-bearing surface and, means for imparting a movement of said array of flux-producing elements relative to said housing.
 2. Apparatus for developing a surface bearing a latent electrostatic image comprising, a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing, means for advancing said surface to be developed in relation to said housing to produce an agitated movement of portions of the developer material within said housing, field-generating means including an array of flux-producing members exterior of said housing adapted for movement relative to said housing for applying alternating magnetic fields to influence portions of the developer material contained therein, and means for producing a movement of said array of flux-producing members relative to said housing to produce an additional agitated movement of the developer material within said housing and enhance development of the image-bearing surface.
 3. Apparatus for developing a surface bearing a latent electrostatic image comprising, a housing containing a quantity of developer material supported adjacent the surface to be developed to create a frictional coupling between said surface and a portion of the developer material in said housing, means for imparting a relative movement between said housing and said surface to be developed to agitate portions of the developer material within said housing into contact with said surface, field-generating means including an array of flux-producing elements positioned in opposing relationship to said housing to allow the image-bearing surface to pass between said housing and said field-gEnerating means, said field-generating means being adapted for movement relative to said housing to apply an alternating magnetic field on said developer material to increase the agitation of the supply of developer material supported in said housing and enhance development of the image-bearing surface, and means for imparting a movement of said array of flux-producing elements relative to said housing.
 4. Apparatus for developing a surface bearing a latent electrostatic image comprising, a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing, means for advancing said surface to be developed in relation to said housing to produce an agitated movement of portions of the developer material within said housing, field-generating means including an array of flux-producing members positioned in opposing relationship to said housing to allow the image-bearing surface to pass between said housing and said field-generating means, said field-generating means being adapted for movement relative to said housing for applying alternating magnetic fields to influence portions of the developer material contained therein, and means for producing a movement of said array of flux-producing members relative to said housing to produce an additional agitated movement of the developer material within said housing and enhance development of the image bearing surface.
 5. Apparatus for developing a surface bearing a latent electrostatic image comprising, a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing, means for advancing the surface to be developed relative to said housing to produce a circulating agitation of the developer material within the housing to develop the image, and magnetic field producing means in cooperative association with said housing for impressing magnetic attractive forces on developer material within said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface.
 6. In an apparatus for developing a surface bearing a latent electrostatic image in which a housing containing a quantity of developer material is supported adjacent the surface to be developed to form a frictional coupling between the surface and a portion of the developer material in the housing, and the surface to be developed is advanced in relation to the housing to produce a circulating agitation of the developer material within the housing to develop the image, the improvement comprising, magnetic field producing means for exerting a magnetic attractive force on developer material within said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface.
 7. Apparatus for developing a surface bearing a latent electrostatic image comprising, a housing containing a quantity of developer material supported adjacent the surface to be developed to form a frictional coupling between said surface and a portion of the developer material in said housing, means for advancing the surface to be developed relative to said housing to produce a circulating agitation of the developer material within the housing to develop the image, magnetic field producing means including an array of flux-producing members in cooperative association with said housing for impressing magnetic attractive forces on developer material within said housing, and means for producing a movement of said array of flux-producing members relative to said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface.
 8. In an apparatus foR developing a surface bearing a latent electrostatic image in which a housing containing a quantity of developer material is supported adjacent the surface to be developed to form a frictional coupling between the surface and a portion of the developer material in the housing, and the surface to be developed is advanced in relation to the housing to produce a circulating agitation of the developer material within the housing to develop the image, the improvement comprising, magnetic field producing means including an array of flux-producing members in cooperative association with said housing for exerting magnetic attractive forces on developer material within said housing, and means for producing a movement of said array of flux-producing members relative to said housing to increase the circulating agitation of the developer material therein and thereby enhance development of the image-bearing surface. 